Iraqi President Fouad Massoum nominated Haider al-Abadi, the deputy parliament speaker, to be the country’s new prime minister on Monday, plunging Iraq into a new wave of political instability as it battles a deadly Islamist insurgency.

The nomination of the Shiite al-Abadi to form a new government cuts short the third term the fellow Shiite Nouri al-Maliki was seeking, the BBC reports. Al-Abadi is also a member of Malilki’s Dawa Party. A group of Iraq’s Shia parties nominated al-Abadi to succeed Maliki, which only added to the humiliation of his ousting.

It’s not yet clear what impact a shift in political power will have on Iraq, a country reeling from the destruction wrought by the offensive of the brutal militant group Islamic State (IS) which has taken the northern city of Mosul and is advancing on the Iraqi capital, Baghdad, and the capital of the Kurdish region, Erbil.

The U.S. has let it be known that they were not prepared to help Iraq in its fight with IS so long as Maliki remained at the helm. Still, in the face of IS gains, President Barack Obama was obliged last week to order airstrikes against advancing IS troops and arm Kurdish forces in the north of Iraq.

The presence of troops in the capital Baghdad on Sunday, including in the Green Zone where many government buildings and the president’s residence are located, could be “part of a power struggle between al-Maliki and Massoum,” CNN reports.

Maliki accused al-Abadi of violating the constitution in a speech on Sunday and said he plans to launch a legal case against his successor. Maliki’s political allies supported him and called al-Abadi’s nomination illegal. As head of the State of Law coalition group, Maliki insists that he should be the one to decide who the next prime minister is, The Washington Postreports.

Pressure has been steadily mounting against Maliki who is widely blamed for allowing IS fighters -- an Islamist group so extreme they have reportedly crucified people and threatened to kill Christians and members of other religious minority groups if they don’t convert to Islam -- to expand their influence in the Sunni-dominated parts of the country.

The U.S. is backing al-Abadi and has warned Maliki that clinging to power would throw Iraq into further chaos. "The government formation process is critical in terms of sustaining stability and calm in Iraq, and our hope is that Mr. Maliki will not stir those waters," Secretary of State John Kerry said from Australia.

The U.S. has tentatively entered the war against IS after President Barack Obama authorized airstrikes against Islamic State fighters and artillery last week. More than 60 extremist fighters have been killed in the strikes, Iraqi officials say.

The U.S. also began directly arming Kurdish forces over the weekend as the region’s peshmerga forces have been unable to hold off IS insurgents, resulting in the around 40,000 Yazidis -- a majority Kurdish-speaking religion based in the northwestern mountains of Iraq combining elements of Islam and ancient faiths Zoroastrianism and Mithraism -- taking refuge on top of Mount Sinjar, in northwest Iraq, battling extreme heat in the daytime and extreme cold at night, with little water, food or medical supplies.

Footage of Britain’s Channel 4 journalist Jonathan Rugman pulling limp and dehydrated Yazidi children to safety on the “Mountain of Death” was published earlier today, illustrating the helplessness and horror of the situation. Rugman also tweeted from the scene.

Unbelievable scenes on mt Sinjar. Saw small families trapped in middle of nowhere. Many of these people will die if not evacuated ASAP.

Around 20,000 Yazidis, a group deemed devil worshippers by IS, were rescued from the mountain on Sunday night and taken to the relative safety of the Syrian-Iraqi border, the Guardianreports. The Kurds used diggers, donkeys, tractors and trucks to transport the refugees, reports the Daily Mail.

American forces have delivered more than 74,000 meals and British and French forces are expected to join them in airdropping much-needed supplies.